Method and system for injection of viscous unweighted, low-weighted, or solids contaminated fluids downhole during oilfield injection process

ABSTRACT

A system for injecting a fluid into a formation including a fluid, and at least one injection pump configured to receive the fluid, the at least one pump including a centrifugal pump having at least two stages configured to increase the pressure of the received fluid is disclosed. The system further includes a drive device coupled to the injection pump. A method of injecting a fluid downhole including providing a fluid to an injection pump, the injection pump including a centrifugal pump having at least two stages, pumping the fluid through the at least two stages of the centrifugal pump, thereby increasing the pressure of the fluid, and injecting the fluid from the injection pump into a wellbore is also disclosed.

This application is a continuation in part of prior PCT/US2008/075814,filed Sep. 10, 2008, which claims priority to U.S. ProvisionalApplication No. 60/972,117, filed Sep. 13, 2007, the disclosures ofwhich are hereby incorporated by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed herein generally relate to a method and system forfluid injection. In particular, embodiments disclosed herein relate to amethod and system for injecting viscous fluids, unweighted fluids,low-weighted fluids, and/or slurries in a downhole formation.

2. Background Art

In the drilling of wells, a drill bit is used to dig many thousands offeet into the earth's crust. Oil rigs typically employ a derrick thatextends above the well drilling platform. The derrick supports jointafter joint of drill pipe connected end-to-end during the drillingoperation. As the drill bit is pushed further into the earth, additionalpipe joints are added to the ever lengthening “string” or “drillstring”. Therefore, the drill string includes a plurality of joints ofpipe.

Fluid or “drilling mud” is pumped from the well drilling platform,through the drill string, and to a drill bit supported at the lower ordistal end of the drill string. The drilling mud lubricates the drillbit and carries away well cuttings generated by the drill bit as it digsdeeper. The cuttings are carried in a return flow stream of drilling mudthrough the well annulus and back to the well drilling platform at theearth's surface. When the drilling mud reaches the platform, it iscontaminated with pieces of shale and rock that are known in theindustry as well cuttings or drill cuttings. Once the drill cuttings,drilling mud, and other drilling effluents containing solid particlesreach the platform, a solids control equipment that may include shaleshakers, desanders, desilters, mud cleaners, and/or oilfield decantercentrifuges, is typically used to remove the drilling mud from the drillcuttings so that the drilling mud may be reused. The remaining drillcuttings, waste, and associated residual drilling fluids are thentransferred to a holding trough for disposal. In some situations, forexample with specific types of drilling fluids, the drilling fluid maynot be reused and it must be disposed of. Typically, the non-recycleddrilling fluid is disposed of separately from the drill cuttings andother waste by transporting the drilling fluid via a vessel to adisposal site.

The disposal of the drill cuttings and drilling mud is a complexenvironmental problem. Drill cuttings contain not only the residualdrilling mud product that would contaminate the surrounding environment,but may also contain oil and other waste that is particularly hazardousto the environment, especially when drilling in a marine environment.

One method of disposing of oily-contaminated cuttings and other drillcutting waste is to re-inject the cuttings into the formation using acuttings re-injection operation. Generally, the injection processinvolves the preparation of a slurry within surface-based equipment andpumping the slurry into a well that extends relatively deep undergroundinto a receiving stratum or adequate formation.

In addition to re-injecting cuttings, it is often necessary to injectother types of fluids downhole during a variety of operations. Forexample, in some cases, it may be necessary to increase the permeabilityof a formation into which waste is injected. One method for increasingformation permeability known in the art is hydraulic fracturing, whereina fluid is forced into the formation to create fractures that extendinto the formation from the borehole. In another application, wellcleaning or treatment fluids may be forced into a wellbore duringregular maintenance or well rehabilitation.

Due to the limited space, it is common to modularize operations and toswap out modules when not needed or when space is needed for theequipment. For example, with respect to cuttings re-injectionoperations, cuttings containers may be offloaded from the rig to makeroom for modularized equipment used for slurrification. These liftingoperations, as mentioned above, are difficult, dangerous, and expensive.Additionally, many of these modularized operations include redundantequipment, such as pumps, valves, and tanks or storage vessels.

Accordingly, there exists a need for more efficient methods of injectinga fluid, or a fluid and a slurry, downhole that require optimized use ofrig deck space.

SUMMARY OF INVENTION

In one aspect, embodiments disclosed herein relate to a system forinjecting a fluid into a formation including a fluid, at least oneinjection pump configured to receive the fluid, the at least one pumpincluding a centrifugal pump having at least two stages configured toincrease the pressure of the received fluid, and a drive device coupledto the at least one injection pump.

In another aspect, embodiments disclosed herein relate to a method ofinjecting a fluid downhole including providing a fluid to an injectionpump, the injection pump including a centrifugal pump having at leasttwo stages, pumping the fluid through the at least two stages of thecentrifugal pump, thereby increasing the pressure of the fluid, andinjecting the fluid from the injection pump into a wellbore.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a slurry or fluid injection system in accordance withembodiments disclosed herein.

FIG. 2 shows a slurry or fluid injection system in accordance withembodiments disclosed herein.

FIG. 3 shows a slurry or fluid injection system in accordance withembodiments disclosed herein.

FIG. 4 shows a slurry or fluid injection system in accordance withembodiments disclosed herein.

FIG. 5 shows a slurry and/or fluid injection system in accordance withembodiments disclosed herein.

FIG. 6 shows a slurry and/or fluid injection system in accordance withembodiments disclosed herein.

FIG. 7 shows a slurry and/or fluid injection system in accordance withembodiments disclosed herein.

FIG. 8 shows a slurry and/or fluid injection system in accordance withembodiments disclosed herein.

FIG. 9 shows a layout for equipment for an injection system inaccordance with embodiments disclosed herein.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein generally relate to a methodor process of cuttings re-injection. In particular, embodimentsdisclosed herein relate to methods and systems for injecting a slurry,viscous bio-polymer based fluids, and/or other associated effluents,into a formation. More specifically, embodiments disclosed herein relateto a method and system for cuttings re-injection using a multi-stagecentrifugal pump.

During cuttings re-injection operations, a slurry is prepared includinga fluid and cleaned drill cuttings. Solid waste, e.g., drill cuttings,is typically degraded, or reduced, to a size of less than 300 microns.The solid waste may be degraded using centrifugal pumps or grindingmachines. Typically, the slurry is prepared by mixing together drillcuttings, previously classified by size, to a desired ratio with afluid, such that a slurry is created that contains a desirablepercentage of drill cuttings to total volume. Those of ordinary skill inthe art will appreciate that generally, the solids content of slurriesused in cuttings re-injection operations is about 20 percent solidscontent by volume. Thus, in a given cuttings re-injection operation, aslurry is prepared for re-injection by mixing drill cuttings with afluid until the solids content of the slurry is about 20 percent. Afterpreparation of the slurry, the slurry is pumped to a vessel for storageuntil a high-pressure injection pump is actuated, and the slurry ispumped from the storage vessel into the wellbore. Rheological propertiesof the slurry may be controlled using polymer additives so that theslurry may be injected under high pressure (typically between 1000 and5000 psi) through a casing annulus or tubular into hydraulic fracturesof suitable formations.

Cuttings re-injection processes include injecting a slurry into aformation using a pump configured to inject the slurry at apre-determined pressure. These pumps often include duplex or triplexpumps. For example, typical injection pumps include a plunger or pistonthat compresses the slurry and injects it downhole at a selectedpressure and pump rate. An example of such a commercially availableplunger pump is an OPI 600 plunger pump from Gardner Denver (Houston,Tex.). The movement of the plunger provides a series of compressions ofthe slurry, thereby pumping the slurry downhole in pulse-like mannerforming specific fractures in a receiving formation. The continualmovement of the plunger and “hammering” of the pumps result in wear ofthe pump components and a noisy working environment. Furthermore,health, safety, and environmental (HSE) issues must be considered whenusing a typical plunger-type pump for cuttings re-injection processes.

Conventional high-pressure pumps and injection systems inject a slurryinto a formation in batches. The movement of the plunger provides aseries of compressions of the slurry, thereby pumping the slurrydownhole in a pulse-like manner, forming specific fractures in areceiving formation. In contrast, the injection system of the presentdisclosure may provide an injection pump that offers continuous andsmooth flow of slurry, because of fundamental differences in thetechnical design of the injection system. Thus, in some embodiments, thesolids content of slurry may be increased. For example, in certainembodiments, the solid content may be approximately 30 percent solidcontent by volume, while the desired injection pressure of the slurry ismaintained. In other embodiments, the slurry may be greater than 30percent solid content by volume. Thus, in some embodiments, a systemusing at least one centrifugal pump may stimulate the receivingformation, allowing stable and more sustainable fracturing. The volumeof waste that may be injected in the formation may therefore beincreased.

One method of injecting a slurry into a formation in accordance withembodiments disclosed herein includes providing a slurry to an injectionpump, pumping the slurry through the injection pump to increase thepressure of the slurry, and delivering or pumping the slurry downholeinto the wellbore. In this embodiment, the injection pump is acentrifugal pump that includes at least two stages, or a multi-stagecentrifugal pump. Each stage of the multi-stage centrifugal pumpincludes an entrance, a stationary diffuser, and an impeller thatrotates and moves the slurry from the entrance to the exit of the stage.As the slurry flows through each stage, the slurry pressure increases.

In another aspect, embodiments disclosed herein generally relate to amethod or process of fluid injection. In particular, embodimentsdisclosed herein relate to methods and systems for injecting a fluidinto a formation. More specifically, embodiments disclosed herein relateto a method and system for fluid injection using at least onemulti-stage centrifugal pump.

Cutting re-injection processes may include not only slurry injection,but also the injection of viscous fluids having no solids content or asmall amount of solids content. Viscous fluids, water portions, andcuttings-containing slurry portions are injected using an alternatinginjection pattern. Additionally, various fluids may be injected into awellbore to prevent and correct problems, and to encourage productivityor absorption in oil, water, or waste wells. Some materials that may bepumped downhole include viscous fluids such as biopolymer based fluids,xanthan gum based fluids, polymer based fluids, and synthetic polymerbased fluids. These and other materials may be used to create viscouspills with properties suitable for operations such as cleaning,formation fracturing, fluid loss control, wellbore treatment, and wasteinjection, among others.

It may also be desirable to inject waste fluids into a waste well. Forexample, during oil production, waste water may be co-produced with theoil which must be separated and disposed of. The waste water, which maycontain hydrocarbons, is often injected into a formation that issufficiently deep and capable of receiving and storing the waste.

One method of injecting a fluid into a formation in accordance withembodiments disclosed herein includes providing the fluid to aninjection pump, pumping the fluid through the injection pump to increasethe pressure of the fluid, and delivering or pumping the fluid into awellbore. In certain embodiments, the injection pump is a centrifugalpump that includes at least two stages, or a multi-stage centrifugalpump. Each stage of the multi-stage centrifugal pump includes anentrance, a stationary diffuser, and an impeller that rotates and movesthe fluid from the entrance to the exit of the stage. As the fluid flowsthrough each stage, the fluid pressure increases.

FIGS. 1-4 show different configurations of injection systems that may beused to inject fluids or slurry in accordance with embodiments disclosedherein. FIGS. 5-8 show different configurations of injection systemsthat may be used to inject a combination of fluids and/or slurries inaccordance with embodiments disclosed herein. FIG. 9 shows an equipmentlayout for a fluid or slurry injection system in accordance withembodiments disclosed herein.

FIG. 1 shows an example of a configuration of an injection system 100 inaccordance with embodiments disclosed herein. The injection system 100may be used as a cuttings re-injection system or as a fluid injectionsystem. As shown, a drive device 104 is coupled to an injection pump102. Drive device 104 may include any device known in the art fordriving a multi-stage centrifugal pump, for example, a direct drive, adiesel drive, a hydraulic drive, a belt drive, a gas drive, a variablefrequency drive (VFD), or an inverter. In the embodiment shown,injection pump 102 is a horizontal centrifugal pump having at least twostages, or multi-stage centrifugal pump. A multi-stage centrifugal pumpis a pump that includes at least two stages, and therefore, at least twoimpellers and at least two diffusers. The impellers and diffusers may bemounted on a single shaft. Bearings, e.g., radial thrust bearings, maybe used to support the shaft in horizontal applications. One of ordinaryskill in the art, however, will appreciate, that a vertically orientedcentrifugal pump having at least two stages may also be used. Duringoperation, the slurry or fluid may enter injection pump 102 at anambient pressure. As the slurry or fluid is pumped through the at leasttwo stages of injection pump 102, the pressure of the slurry or fluidincreases. When the slurry or fluid exits the diffuser of the last stageof the injection pump 102, the slurry or fluid may be pumped through avalve or manifold (not shown) and then pumped downhole (indicated at110) and into wellbore 106.

One of ordinary skill in the art will appreciate that injection pump 102may include as many stages as necessary to achieve the desired increasein pressure, or pre-determined injection pressure. For example, themulti-stage centrifugal pump may include 2 stages, 5 stages, 15 stages,17 stages, 19 stages, or any number of stages necessary to provide thedesired injection pressure. Additionally, the size of the centrifugalpump and the number of stages of the centrifugal pump may be selectedbased on the desired pump rate and pressure of the slurry or fluid forinjection downhole. For example, in addition to the number of stages,the size of the bore of the multi-stage centrifugal pump may be selectedto obtain a desired pressure and pump rate. In certain embodiments, thecentrifugal pump may have a 4 inch bore, a 6 inch bore, an 8 inch bore,or any other size known and used in the art. Thus, in one embodiment,injection pump 102, in accordance with embodiments disclosed herein, maydeliver, for example, 10 bbl/min of slurry at 1500 psi.

In an alternative embodiment, as shown in FIG. 2, an injection system200 may be used as a cuttings re-injection system or a fluid injectionsystem. The injection system 200 includes an injection pump 202, a drivedevice 204 coupled to the injection pump 202, and a second centrifugalpump 208. In this embodiment, injection pump 202 is a horizontalcentrifugal pump having at least two stages, or horizontal multi-stagecentrifugal pump. Secondary centrifugal pump 208 may be disposed before(i.e., upstream of) injection pump 202, and may include a singleentrance, a single diffuser, and a single impeller (not independentlyillustrated). The secondary centrifugal pump 208 may receive the slurryor fluid from, for example, a holding tank or vessel (not shown), andmay pump the slurry or fluid through a valve or manifold (not shown) toinjection pump 202 at a pressure greater than ambient pressure. That is,as the slurry or fluid is pumped through the secondary centrifugal pump208, the pressure of the slurry or fluid may increase to a pressureabove ambient pressure. Thus, secondary centrifugal pump 208 acts like abooster pump to increase the pressure of the slurry or fluid to adesired pressure before transferring the slurry or fluid to theinjection pump 202. Next, as the slurry or fluid is pumped through theat least two stages of the injection pump 202, the pressure is furtherincreased until a pre-determined injection pressure and/or pump rate isachieved. When the slurry or fluid exits the last stage of the injectionpump 202, the slurry or fluid may be pumped through a valve or manifold(not shown) and then pumped downhole (indicated at 210) and intowellbore 206.

Referring now to FIGS. 3 and 4, injection systems 300 and 400, inaccordance with embodiments disclosed herein, may be used for cuttingsre-injection or fluid injection. The injection systems 300 and 400include an injection pump 302, 402 which may be a vertically orientedcentrifugal pump having at least two stages, or vertical multi-stagecentrifugal pump. Each stage of the multi-stage centrifugal pumpincludes an entrance, a diffuser, and an impeller that rotates and movesthe slurry from the entrance to the exit of the stage. As the slurry orfluid flows through each stage, the slurry or fluid pressure increases.The injection pump 302, 402 may be configured such that a pre-determinedpressure and/or pump rate of the slurry or fluid injected downhole(indicated at 310, 410) is achieved. For example, the number of stagesand the size of the multi-stage centrifugal pump may be selected suchthat a pressure and pump rate of slurry or fluid suitable for aspecified injection operation is achieved. When the slurry or fluidexits the last stage of the injection pump 302, 402 the slurry or fluidmay be pumped through a valve or manifold (not shown) and then pumpeddownhole (indicated at 310, 410) and into wellbore 306, 406.

Further, as shown in FIG. 4, a secondary centrifugal pump 408 may beprovided before (i.e., upstream of) the injection pump 402, and mayinclude a single entrance, a single diffuser, and a single impeller (notindependently illustrated). Secondary centrifugal pump 408 may receivethe slurry or fluid from, for example, a holding tank or vessel (notshown), and pump the slurry or fluid to injection pump 402 at a pressuregreater than ambient pressure. That is, as the slurry or fluid is pumpedthrough secondary centrifugal pump 408, the slurry or fluid pressure mayincrease to a pressure above ambient pressure. Thus, the secondarycentrifugal pump 408 acts as a booster pump to increase the pressure ofthe slurry or fluid to a desired pressure before transferring the slurryor fluid to injection pump 402. Next, as the slurry or fluid is pumpedthrough the at least two stages of injection pump 402, the slurry orfluid pressure is further increased until a pre-determined injectionpressure and/or pump rate is achieved.

Referring now to FIG. 5, another example of a configuration of aninjection system 500 in accordance with embodiments disclosed herein isshown. A tank or storage container 502 may provide fluid and/or slurryto a secondary pump 504. The secondary pump 504 shown is a centrifugalpump, but other types of pumps may also be used. The secondary pump 504may include a single entrance, a single diffuser, and a single impeller(not independently illustrated). Secondary pump 504 acts like a boosterpump to increase the pressure of the fluid and/or slurry to a desiredpressure before transferring the fluid and/or slurry through a valve ormanifold 506. The valve or manifold 506 may direct the fluid and/orslurry to one or both of injection pumps 508, 510 which may be disposedin parallel. One of ordinary skill in the art will appreciate that twoor more pumps may be disposed in parallel without departing from thescope of embodiments disclosed herein. The fluid and/or slurry may thenpass from one or both of the injection pumps 508, 510 through a secondvalve or manifold 512 and into the borehole, as indicated by arrow 514.

The injection pump 508 shown in FIG. 5 is a multi-stage centrifugal pumpshown in a horizontal orientation; however, one of ordinary skill in theart will appreciate that a vertically oriented multi-stage centrifugalpump may also be used, as discussed above. One of ordinary skill in theart will appreciate that injection pump 508 may include as many stagesas necessary to achieve the desired increase in pressure of the fluidand/or slurry, or pre-determined injection pressure. For example, themulti-stage centrifugal pump may include 2 stages, 5 stages, 15 stages,17 stages, 19 stages, or any number of stages necessary to provide thedesired injection pressure. Additionally, the size of the centrifugalpump and the number of stages of the centrifugal pump may be selectedbased on the desired pump rate and pressure of the fluid and/or slurryfor injection downhole. For example, in addition to the number ofstages, the size of the bore of the multi-stage centrifugal pump may beselected to obtain a desired pressure and pump rate. In certainembodiments, the centrifugal pump may have a 4 inch bore, a 6 inch bore,an 8 inch bore, or any other size known and used in the art.

The injection pump 510 shown may be a plunger or piston pump, or anyother type of pump known in the art. In certain embodiments, theinjection pump 510 may be a duplex or triplex pump. In one embodiment, afluid having low solids content may be pumped through the multi-stagecentrifugal injection pump 508, and a slurry may be pumped through theinjection pump 510. As used herein, a low solids content fluid refers toa fluid that may have some suspended particles entrained therein or nosolid suspended items. Specifically, in select embodiments, a low solidscontent fluid may include less than 5 percent solid content forundissolved solids. For dissolved solids, the percent of solid contentmay be increased, forming saturated and/or oversaturated solutions,until the percent of undissolved solids reaches, for example, 5 percent.Thus, as used herein, low solids content fluids may include bothundissolved solids and dissolved solids. As discussed above, theinjection pumps 508, 510 may have different sizes and/or stagesconfigured to provide a desired pressure and pump rate. Further, one ofordinary skill in the art will appreciate that, during operation of theinjection system 500, either one or both of the injection pumps 508, 510may be used.

In this embodiment, low solids content fluids such as, for example,polymer-based fluids, xanthan gum-based fluids, biopolymer-based fluids,synthetic polymer-based fluids, hydrocarbon-based fluids, viscouspill-fluids, waste fluids, water-based fluids, water, or salt water, maybe pumped through the centrifugal pump while heavier solids contentfluids, i.e., slurries, are pumped through a plunger pump. Additionally,in certain embodiments, a low solids content fluid may includeunweighted fluid, which means that no weighting material has been addedthereto. In one embodiment, the pumps may be run in an alternatingsequence while in other embodiments the pumps are run simultaneously.

A specific embodiment encompassed by the injection system 500 of FIG. 5is shown in FIG. 6. In the injection system 600, both injection pumps608, 610 may be multi-stage centrifugal pumps. One of ordinary skill inthe art will appreciate that one or both of the injection pumps 608, 610may be oriented vertically as shown in FIGS. 7 and 8, respectively. Eachstage of the multi-stage centrifugal pumps 608, 610 includes anentrance, a diffuser, and an impeller that rotates and moves the fluidfrom the entrance to the exit of the stage. As the slurry or fluid flowsthrough each stage, the pressure thereof increases. The two injectionpumps 608, 610 may each comprise a different number of stages and may bedifferent sizes as needed to produce desired output pressures. Forexample, the injection pump 608 may have 2 stages while the injectionpump 610 may have 15 stages. Additionally, one of ordinary skill in theart will appreciate that, during operation of the injection system 600,either or both of the injection pumps 608, 610 may be used, as discussedabove.

The vertical configuration/placement of the injection pumps 302, 402shown in FIGS. 3 and 4, and at least one of the injection pumps 608, 610shown in FIGS. 7 and 8, provides a reduced foot print on the rig deck.In one embodiment, at least one vertically oriented injection pump maybe placed on the side of a rig deck with the use of, for example, a slipor guide holder. In this embodiment, injection pumps 302, 402, 608, 610may require little or no deck space. One of ordinary skill in the artwill appreciate that the injection systems 700 and 800 may be easilyre-configured to accommodate a vertical or horizontal injection pump ofa type other than a multi-stage centrifugal injection pump.

In one embodiment, the shafts, bearings, impellers and/or diffusers ofthe at least two stages of the multi-stage centrifugal pumps discussedabove may be formed from materials known in the art to reduce the wearand increase the life of pump components. For example, the shafts,bearings, impellers and/or diffusers may be formed from a ferritic steelmaterial, a ceramic material or a composite material comprising nickel,chrome, and silicone (i.e., NiResist™, 5530 alloy). Additionally, theimpellers and/or diffusers may be coated with a wear-resistant materialto reduce wear on the pump components, thereby extending the life of themulti-stage centrifugal pump. For example, a polymer-based coating(e.g., polyurethane), a ceramic coating, or a metal coating (e.g.,tungsten carbide) may be applied to the impeller and/or diffuser.

Examples of commercially available multi-stage centrifugal pumps thatmay be used in accordance with embodiments of the present disclosureinclude a RedaHPS™ multistage centrifugal pump available from, forexample, Schlumberger (Houston, Tex.), Wood Group (Houston, Tex.), orRentzel Pump Manufacturing (Norman, Okla.), an electrical submersiblepump (ESP), or an artificial lift pump. These multi-stage centrifugalpumps may be configured in a horizontal or vertical orientation, asdiscussed above, as determined by the amount of available rig deck spaceavailable. These multi-stage centrifugal pumps may also be coupled to adrive device, such as a direct drive, belt drive, variable speed drive,variable frequency drive, inverter, or gas drive. Additionally, themulti-stage centrifugal pump may be fluidly connected to a tank orvessel containing slurry, such that the slurry may be pumped downholeand injected into the formation fractures.

Testing of an injection system, specifically a cuttings re-injectingsystem for injecting a slurry, in accordance with embodiments disclosedherein was performed and analyzed. Additionally, a conventional triplexpump was also tested for injecting a slurry into a formation. The testresults confirmed that the injection system formed in accordance withembodiments disclosed herein injected viscous and weighted waste slurryin a continuous and smooth manner rather than in a pulsed manner ofdelivering the slurry provided by the conventional triplex pump. Acontinuous and smooth injection of the slurry or fluid may be importantfor production waste injection and may allow injection of a slurry withincreased solids content.

The tested system for injection of a slurry into a formation inaccordance with the present disclosure included a 44-stage centrifugalpump. The 44-stage centrifugal pump was positioned in a horizontalorientation. The tested 44-stage centrifugal pump system was used toinject high viscosity (i.e., at least 60 second/quart Marsh funnelviscosity) slurry with a density of 1.27 gram/cm³.The slurry injectedincluded particles with an average size range of between 100 microns and300 microns. An example of the equipment arrangement for the testingsystem is shown in FIG. 9. A system with a horizontal multi-stagecentrifugal pump, indicated at 950, and a conventional system with atriplex pump, indicated at 960, is shown. Additional equipment used intesting the systems may include a slurry unit 952, shakers or otherseparatory means 954, pneumatic transfer devices 956, storage tanks 958,and an injection manifold 962. Several parameters of the slurryinjection systems are shown in Table 1 and parameters of the sea waterinjection systems are shown in Table 2.

TABLE 1 Parameters for a System using a Triplex Pump and a System usinga Centrifugal Pump for Slurry Injection System using a 44-Stage SlurryInjection System using a Triplex Pump Centrifugal Pump Rate of injectionof slurry and 3.4 bpm @ 1000 psi 7.8 bpm @ 2300 psi maximum pressureInjection time for 600 bbl of 3 hours 1 hour 30 min slurry PumpParameters Maximum output: 400 BHP Motor: Toshiba600 HP Maximum speed:350 RPM Length: 32.2 ft. Plunger diameter: 3 in. Height: 2.71 ft. Strokelength: 6 in. Suction: 6 in. Planetary Gear Ratio: 4.68:1 Discharge: 4in. Maximum pressure: 8490 psi Digital Control: Variable Frequency Drive(VFD)

TABLE 2 Parameters for a System using a Triplex Pump and a System usinga Centrifugal Pump for Sea Water Injection System using a 44-Stage SeaWater Injection System using a Triplex Pump Centrifugal Pump Rate ofinjection of sea water and 3.3 bpm @ 2000 psi 4.2 bpm @ 2200 psi maximumpressure Injection time for 1000 bbl of sea 5 hours 4 hours 40 min waterPump Parameters Maximum output: 400 BHP Motor: Toshiba 600 HP Maximumspeed: 350 RPM Length: 32.2 ft. Plunger diameter: 3 in. Height: 2.71 ft.Stroke length: 6 in. Suction: 6 in. Planetary Gear Ratio: 4.68:1Discharge: 4 in. Maximum pressure: 8490 psi Digital Control: VFD

During offshore trials, a Reda HPS™ centrifugal pump was used and an OPITriplex plunger pump was used. Using the parameters listed in Table 1and Table 2, the injection profiles between the plunger pump system andthe centrifugal pump system showed significant differences. For the samevolume of fluid (600 bbls slurry/1000 bbls sea water), the centrifugalpump system completed the batch faster. Additionally, the centrifugalpump system maintained an elevated well pressure of at least 2200 psiduring the slurry injection. The slurry output of the centrifugal pumpsystem was significantly greater than the standard plunger pump system.It was also noted that the centrifugal pump system required less dailymaintenance, and that the digital control of the VFD on the centrifugalpump system allowed precise setting of the pump's output. Samples takenat the outlets of both the centrifugal pump system and the plunger pumpsystem revealed that slurry properties were similar, but that in somecases, the centrifugal pump system produced a slurry with a higher MarshFunnel viscosity. Higher Marsh Funnel viscosity numbers may create amore stable slurry and may provide benefits including improvedingredients dispersion and improved suspension of solid particles in thepolymer matrix of the slurry.

In view of the above, a centrifugal pump system, in accordance withembodiments disclosed herein, may be used for various waste injectionapplications. For example, a centrifugal pump system may be used to pumpslurry downhole. Alternatively, a centrifugal pump system may be used topump fluids with low solids content. In some embodiments, a plunger pumpsystem may be used in conjunction with a centrifugal pump system,wherein, for example, the plunger pump system is used to pump a slurrydownhole and the centrifugal pump system is used to pump a low solidscontent fluid downhole.

Advantageously, embodiments disclosed herein provide a method and systemfor fluid and/or slurry injection that may reduce the amount of requiredrig deck space for both a fluid injection system and fluid holdingtanks/vessels. Furthermore, an injection system in accordance withembodiments disclosed herein may be configured in either a horizontal orvertical orientation, thereby providing more flexibility in thearrangement of the system.

Additionally, in certain embodiments, potential installation costs andstructural support problems may be minimized, because the deck load orweight of the necessary equipment or components for the cuttingsre-injection system may be less than that of conventional fluidinjection systems. In certain embodiments, the deck load may be reducedby more than 50 percent as compared to conventional systems. Inaddition, injection pumps in accordance with embodiments disclosedherein, e.g., multi-stage centrifugal pumps, may require less up-frontcost (e.g., a 20 percent reduction) and shorter up-front delivery times(e.g., 25 percent reduction) than other injection pumps, e.g., plungerpumps.

Injection pumps for fluid or slurry injection in accordance withembodiments disclosed herein may provide extended run times due to theunique impeller/diffuser staging system of a multi-stage centrifugalpump, which may be calculated in terms of years rather than days ormonths of conventional injection pumps. Additionally, drilling wastes orslurries with higher viscosity (e.g., approximately 100 cP or higher)and higher density (e.g., approximately 1.15 gram/cm3 or higher) thanwaste injected by conventional systems may be injected into a formationwith the system and equipment formed in accordance with the presentdisclosure. Maintenance of an injection pump in accordance withembodiments disclosed herein may also be faster and more efficient, asthe time to replace parts or change out the pump may be shorter. Thus,downtime of an injection pump due to maintenance may be minimized andrun life extended.

Further, an injection pump in accordance with embodiments disclosedherein may improve the QHSE (quality, health, safety, and environment)of an injection system, because it may eliminate the hammering orpulsation of conventional high pressure lines, plunger pumps, andinjection pump systems, thereby reducing wear on the equipment. Aninjection system in accordance with embodiments disclosed herein mayalso be more consistent in use, allowing less reliance on outsideexpertise. Additionally, an injection pump as discussed above mayadvantageously be powered by various kinds of drive systems, forexample, VFD, direct by electric, diesel, or hydraulic, or remotely. Incertain embodiments, the injection system may be remotely monitoredand/or controlled using an office live-feed of the system activities.

Fluid injection systems in accordance with embodiments described hereinmay also advantageously provide more sensitive formation injection thana conventional plunger pump injection system. In particular, because aninjection pump system in accordance with embodiments discussed aboveincludes a multi-stage centrifugal pump, the flow of slurry or fluid maybe continuous and smooth, rather than pulsating. Because a multi-stageinjection pump, as described above, provides for a continuous flow ofslurry or fluid, injection time may be reduced and the size of a slurryor fluid holding tank/vessel may also be reduced, further reducingrequired deck space. Additionally, the smooth flow of slurry or fluidmay increase the receiving capacity of the receiving formation bymaintaining sufficient fractures, thereby increasing permeability of thereceiving formation.

Further, economic advantages may be provided by an injection system thatuses centrifugal pumps for fluids, and duplex or triplex pumps forslurries. Centrifugal pumps may be used to inject fluids that have lowsolids content without sustaining significant damage to the centrifugalpump components. Similarly, duplex or triplex pumps may be used toinject slurries that have high solids content without subjecting theduplex or triplex pump components to extensive and destructive wear. Asystem using at least one centrifugal pump may require less maintenanceand, thus, reduced labor and downtime for maintenance. As a result,improved HSE conditions, in addition to time and cost savings, may beachieved.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed:
 1. A method of injecting a fluid downhole, the methodcomprising: diverting a fluid along a common flow path to one of acentrifugal pump and a plunger pump, the plunger pump disposed in thecommon flow path parallel to the centrifugal pump, wherein the fluidcomprises one of a first solids fluid having less than 5 percentundissolved solids and a second solids fluid having greater than 5perfect undissolved solids; pumping the fluid through one of thecentrifugal pump and the plunger pump, the pumping comprising increasingthe pressure of the fluid to an injection pressure greater than a wellpressure, wherein the first solids fluid is diverted and pumped throughthe centrifugal pump and the second solids fluid is diverted and pumpedthrough the plunger pump; and injecting the pressurized fluid into awellbore.
 2. The method of claim 1, further comprising: providing athird injection pump disposed upstream of the centrifugal pump and theplunger pump; and pumping the fluid through the third injection pump toat least one of the centrifugal pump and the plunger pump.
 3. The methodof claim 1, wherein the first solids fluid comprises at least one of agroup consisting of biopolymer-based fluid, xanthan gum-based fluid,synthetic polymer-based fluid, polymer-based fluid, hydrocarbon-basedfluid, water-based fluid, water, and salt water.
 4. The method of claim1, wherein the first solids solids content fluid is unweighted.
 5. Themethod of claim 1, wherein the centrifugal pump provides a continuousflow of slurry.
 6. The method of claim 1, wherein the plunger pumpprovides a pulsating flow of fluid.
 7. A system for injecting a fluidinto a formation comprising: a first manifold having an outlet; acentrifugal pump having at least two stages; a plunger pump disposed inparallel with the centrifugal pump; and a second manifold having aninlet; the outlet of the first manifold fluidly connected to an inlet ofthe centrifugal pump and an inlet of the plunger pump; the inlet of thesecond manifold fluidly connected to an outlet of the centrifugal pumpand an outlet of the plunger pump further comprising valves forselectively diverting a first solids fluid have an undissolved solidscontent under a threshold to the centrifugal pump and a second solidsfluid having an undissolved solids content over the threshold to theplunger pump.
 8. The system of claim 7, wherein the centrifugal pump hasbetween 10 and 60 stages.
 9. The system of claim 8, wherein thecentrifugal pump has 44 stages.
 10. The system of claim 7, wherein thecentrifugal pump and the injection pump are oriented horizontally. 11.The system of claim 7, wherein the centrifugal pump and the injectionpump are oriented vertically.